The effects of nursery length and pond substrate use in production of freshwater prawn Macrobrachium rosenbergii

by 1981- Marlowe, Holly Alford

Pond production of freshwater prawn (Macrobrachium rosenbergii) is limited in temperate regions by the length of the growing season. The indoor nursery phase is intended to increase the growing season, but can be costly to maintain. This study compared the total weight and survival (%) of prawn grown indoors for 30 days to prawn grown indoors for 60 days. Artificial substrate was used in the nursery tanks to increase yield and survival of the post-larvae. The prawn nursed for 60 days were stocked at 4.6 prawn/L of water and the prawn nursed for 30 days were stocked at 4.75 prawn/L; the mean weight of all postlarvae at the beginning of the study was 0.01 g. The 60-day group was significantly larger at the end of the nursery experiment than the 30-day group (average individual weight was 0.12 g, compared to 0.07 g). Prawn were stocked at two sites in Tennessee with six 0.04-ha outdoor ponds at each site. The ponds at one site used artificial substrate and were stocked at 27,375 prawn/ha (10,950 prawn/acre), while ponds at the other site did not have artificial substrate and were stocked at 30,000 prawn/ha (12,000 prawn/acre). After approximately 120 days, the prawn were harvested, weighed, and counted. The ponds with artificial substrate had significantly increased survival between the 30-day group and the 60-day group (82% and 88%, respectively). The total weight between the treatments was significantly different with 76.4 kg (168.5 lbs) for the 30-day group and 108.2 kg (238.5 lbs) for the 60day group. The survival in the ponds without substrate was 81% for the 30-day iii group and 76% for the 60-day group and was not statistically significant. The total weight between the treatments was not significantly different with 99.7 kg (219.7 lbs) for the 30-day group and 100.7 kg (222.1 lbs) for the 60-day group. Stocking post-larvae nursed for 60 days results in a larger yield and higher survival than those nursed for 30 days if artificial substrate is used in the ponds. There is little difference in total yield between stocking post-larvae reared for 30 versus 60 days if artificial substrate is not used. The reduced survival in the 60day group without substrate is likely due to increased cannibalism as a result of the increased size compared to available substrate surface area. iv